1. Field of the Invention
The present invention relates to a scanned image correcting apparatus for correcting the displacements of scan positions in scanned image data (image signals) that are scanned by a plurality of line image sensors (scan means), an image scan apparatus such as a scanner equipped with such a scanned image correcting apparatus, and an image forming apparatus such as a copier machine, a multifunctional machine, or a facsimile machine that is equipped with such an image scan apparatus.
2. Description of the Related Art
In a conventional image scan apparatus such as a scanner, as shown in FIG. 6, a color image sensor (i.e., three-line color CCD) 207 is used to perform a scan where the color image sensor 207 includes individual line sensors 10r, 10g, and 10b corresponding to R, G, and B. The line sensors 10r, 10g, and 10b corresponding to R, G, and B are arranged in parallel at intervals each equal to a predetermined pitch L.
Since the line sensors 10r, 10g, and 10b are arranged in parallel at the predetermined pitch L, scan positions are displaced between the R, G, and B colors by a shift amount corresponding to the predetermined pitch L when a document image is scanned. This can be understood from FIG. 5, in which the document image is scanned from the left to the right (in the sub-scan direction). Namely, the scan positions are displaced by n lines between R and G and between G and B in the sub-scan direction. In order to correct these displacements, with FIG. 5 being used as an example, the R image data that is scanned first is delayed by 2n lines, and the G image data that is scanned next is delayed by n lines, so that these R and G image data are aligned with the B image data that is scanned last. This inter-line correction process eliminates the displacements.
The line interval n between the sensors, however, varies depending on the scan speed of the document image in the sub-scan direction, which is determined by the scan resolution of the image scan apparatus.
In the following, an image scan apparatus with the line sensor interval L corresponding to a scan interval of 4 600-dpi lines will be used as an example.
When the image scan apparatus scans an image at 600 dpi, the displacement between R and B is 8 lines, and the displacement between G and B is 4 lines, as shown in FIG. 31. In this case, the pitch L between the line sensors 10r, 10g, and 10b corresponding to R, G, and B is an integer multiple of the 1-line scan interval. In this case, the displacements of scan positions can be corrected by performing the inter-line correction process in the same manner as in the related-art arrangement.
When this image scan apparatus scans an image at 400 dpi, on the other hand, scan speed in the sub-scan direction is 3/2 of that of 600 dpi, so that the 1-line scan interval is also 3/2 of that of 600 dpi. Because of this, the displacement between R and B is 16/3 lines, and the displacement between G and B is 8/3 lines, as shown in FIG. 32. In this case, the pitch L between the line sensors 10r, 10g, and 10b corresponding to R, G, and B is not an integer multiple of the 1-line scan interval. In such a case, there is a problem in that a displacement corresponding to a fraction of one line remains after delaying the R image data and G image data by an integer multiple of the 1-line scan interval as in the related art.
In consideration of this, there is a known technology that uses a delay unit 22 for an integer delay and an interpolation unit 23 for a decimal delay so as to correct a displacement for a decimal delay that remains as an uncorrectable error after the delay by an integer multiple as described above (e.g., see Patent Document 1). In order to perform a delay corresponding to 2.6 lines, for example, the delay unit 22 performs an integer delay corresponding to 2 lines, and the interpolation unit 23 takes care of a decimal delay corresponding to 0.6 lines.    [Patent Document 1] Japanese Patent Application Publication No. 9-270898
In the technology disclosed in Patent Document 1, when the size of the displacement of scan positions is Nd lines at the maximum, e.g., 10 lines at the maximum, a memory is necessary that can temporarily store data for 10 lines for the purpose of correcting the integer-multiple displacement. If the intervals of the RGB line sensors are wide, or if the scan resolution is high, there is a problem of the required memory size being increased.
Accordingly, there is a need for a scheme that can reduce the memory size required for the correction of displacement of scan positions.